Ten homes in Sheffield belonging to asthma sufferers were cleaned and ventilated to reduce their humidity to levels found 4,000 metres up in the Alps. Their occupants were followed for a year and compared with those from 20 other homes.
Researchers from the Royal Hallamshire Hospital in Shef-field, who measured the residents' breathing at five intervals over the year, found the improvement was equivalent to a daily dose of 400 micrograms of inhaled asthma drugs. If the experiment can be repeated on a wider scale it could mean thousands of asthma patients might be helped to do without drugs.
The results are to be presented to a meeting of the British Thoracic Society today. Dr Michael Pearson, a spokesman for the society and a specialist in asthma at Aintree Hospital, Liverpool, described the pilot study as "one of the most exciting developments we have seen."
He added: "If this really works the prospects of helping significant numbers of asthmatics are very good. We hear a lot about new treatments but this has promise beyond the usual."
An estimated 3.4 million people suffer from asthma in Britain and there are 85,000 hospital admissions for the condition a year. The numbers affected have been rising since the 1960s but doctors do not understand why. In up to half of patients asthma is triggered by house dust mites and researchers have sought to reduce their presence in the home by frequent vacuuming, washing and encasing bedding in impermeable covers.
The new technique is based on the observation that house dust mites cannot survive at high altitudes because the humidity is too low. By simulating the atmosphere of an alpine chalet, patients can be helped to breathe more easily.
In Sheffield intensive cleaning, involving steam treatment of mattresses, bedding and carpets using specialist equipment, was designed to eliminate mites, and the installation of a fan with a filter in bedrooms was intended to improve ventilation to keep the humidity low so they did not return.
Tim Higenbottam, professor of medicine at the University of Sheffield and the Royal Hallamshire Hospital, who led the study, said: "This treatment is about dropping the mite numbers and the allergens they produce to zero." The intensive cleaning costs pounds 500 for an average house. The fan and filter cost a further pounds 100. Professor Higenbottam said: "It is quite a lot of money but the cost of drugs for the average asthmatic is pounds 400 to pounds 500 a year. The ideal is to reduce the numbers who have to take drugs."
The research was funded by a specialist cleaning company, Mediclean of Leeds. Most asthma studies were funded by drug manufacturers or other companies with a commercial interest, Professor Higenbottam said.
A spokesman for the National Asthma Campaign said the findings were promising but the cost could prove prohibitive. A wider study was needed. "There are simpler things that people can do which are effective, such as damp dusting, hot washing bedding at 60C and putting children's soft toys in the freezer before washing every two weeks," he said.